Why are Earth's oldest baobab trees dying?

Baobab trees are ancient, iconic structures with stalky branches that jut out haphazardly from rugged, thick trunks. These odd-looking trees can grow to an enormous size and are found in low-lying areas in Africa and Australia.

Baobabs are sometimes known as upside-down trees because their spindly branches look like roots reaching up to the sky. The iconic trees are also called monkey bread trees because of their plentiful fruit.

Until recently, these trees seemed nearly indestructible. People have used their cavernous trunks for homes, shops, storage and even a cocktail bar.

But then they began to topple. In early 2016, the Sunland baobab in Modjadjiskloof, South Africa — which had grown to an impressive 62 feet tall and nearly 112 feet in girth — began to split. By late 2017, it had collapsed completely.

The Sunland baobab, also called the Platland tree, had been functioning as a cocktail bar. Some thought perhaps all those people visiting the tree's innards may have been the reason for its demise. But it wasn't the only baobab that crumbled.

Explaining the sudden collapse

A large number of the oldest and largest baobabs in Africa have died within the last 12 years, researchers report in a new study in the journal Nature Plants. They found that nine of the 13 oldest have died, or are near death, having lost their oldest parts/stems, over the past 12 years.

"Such a disastrous decline is very unexpected," study coauthor Adrian Patrut, a chemist at Romania's Babeș-Bolyai University, tells NPR. "It's a strange feeling, because these are trees which may live for 2,000 years or more, and we see that they're dying one after another during our lifetime. It's statistically very unlikely."

Researchers aren't sure if this is the first time baobabs have died off in this way. When these trees decay, they do it quickly and rarely leave many traces behind. Scientists aren't sure what the cause of death is yet, but they suspect changing climate may be to blame.

"When around 70 percent of your 1,500- to 2,000-year-old trees died within 12 years, it certainly is not normal,” Erika Wise from the University of North Carolina, Chapel Hill, tells the Atlantic. “It is difficult to come up with a culprit other than climate change.”